A characteristic of a memory may depend on an environment where the memory is located, the number of times that the memory has been used, and a lapse of time between uses. In a memory system, a data skew may occur on a memory interface due to a change in voltage or a change in environment.
To reduce the data skew and latch data in a stable manner, the memory system may calibrate a data strobe clock signal. For example, through the calibration, the memory system may place the data strobe signal at the center of a timing margin of a data signal.
The memory system may perform the calibration operation before making a request to the memory device for a read operation and a write operation (initial training). However, the calibration operation that is performed before the read operation and the write operation may fail to improve the timing margin reduced due to an environment in which the memory system (or memory device) is used.